Constraints on a Primordial Magnetic Field

We derive an upper limit of $B_0<3.4\times 10^{-9}(\Omega_0h_{50}^2)^{1/2}$ Gauss on the present strength of any primordial homogeneous magnetic field. The microwave background anisotropy created by cosmological magnetic fields is calculated in the most general flat and open anisotropic cosmologies containing expansion-rate and 3-curvature anisotropies. Our limit is derived from a statistical analysis of the 4-year Cosmic Background Explorer data for anisotropy patterns characteristic of homogeneous anisotropy averaged over all possible sky orientations with respect to the COBE receiver. The limits we obtain are considerably stronger than those imposed by primordial nucleosynthesis and ensure that other magnetic field effects on the microwave background structure are unobservably small.Comment: 4 pages, uses RevTex, submitted to PR

Democratic citizenship-in-the-making: dis/engagement profiles of portuguese youth

Coming to terms with the multidimensionsionality of civic and political engagement implies analyzing it in a comprehensive manner: not limited to conventional modes of expression, nor to dichotomic perspectives or observable acts of participation. Studies in this field tend to overlook cognitive and emotional dimensions as types of engagement which, alongside with behavior, constitute citizenship. In this article, we analyze data from the Portuguese sample of the CATCH-EyoU Project’s survey (1,007 young people aged between 14 and 30 years old). The main result is the identification of four distinct profiles according to behavioral, emotional and cognitive forms of engagement: Alienated, Passive, Disengaged and Engaged. These profiles are then examined to assess whether and how they differ in terms of: i) national and European identification, ii) relationships with alternative and traditional media, iii) democratic support, and iv) attitudes towards immigrants and refugees. The relationship between the different profiles and individual socio-demographic variables is also examined. We discuss how different dis/engagement profiles relate with socio-political dimensions and have different consequences both in terms of the political integration of young people and of the political challenges faced by democratic societies

The linear growth rate of structure in Parametrized Post Friedmannian Universes

A possible solution to the dark energy problem is that Einstein's theory of general relativity is modified. A suite of models have been proposed that, in general, are unable to predict the correct amount of large scale structure in the distribution of galaxies or anisotropies in the Cosmic Microwave Background. It has been argued, however, that it should be possible to constrain a general class of theories of modified gravity by focusing on properties such as the growing mode, gravitational slip and the effective, time varying Newton's constant. We show that assuming certain physical requirements such as stability, metricity and gauge invariance, it is possible to come up with consistency conditions between these various parameters. In this paper we focus on theories which have, at most, 2nd derivatives in the metric variables and find restrictions that shed light on current and future experimental constraints without having to resort to a (as yet unknown) complete theory of modified gravity. We claim that future measurements of the growth of structure on small scales (i.e. from 1-200 h^{-1} Mpc) may lead to tight constraints on both dark energy and modified theories of gravity.Comment: 15 Pages, 11 Figure

Rotatory power reversal induced by magnetic-current in bi-isotropic media

Bi-isotropic media constitute a proper scenario for scrutinizing optical effects stemming from magnetoelectric parameters. Chiral magnetic current is a macroscopic effect arising from the chiral magnetic effect that enriches the phenomenology of a classical dielectric medium. This work examines optical aspects of bi-isotropic media in the presence of magnetic conductivity. The full isotropic scenario manifests circular birefringence described by a dispersive rotatory power that changes sign at a given frequency. For a bi-isotropic medium with antisymmetric magnetic conductivity, an intricate dispersive rotatory power is attained, supplied with sign reversal as well. This scenario also indicates a handedness reversion of the medium, an unusual property in dielectrics, which may work as a signature of bi-isotropic media supporting chiral magnetic current.Comment: 9 pages, 3 figure

The effect of subscription video-on-demand on piracy: evidence from a household-level randomized experiment

We partner with a major multinational telecommunications provider to analyze the effect of subscription video-on-demand (SVoD) services on digital piracy. For a period of 45 consecutive days, a group of randomly selected households who used BitTorrent in the past were gifted with a bundle of TV channels with movies and TV shows that could be streamed as in SVoD. We find that, on average, households that received the gift increased overall TV consumption by 4.6% and reduced Internet downloads and uploads by 4.2% and 4.5%, respectively. However, and also on average, treated households did not change their likelihood of using BitTorrent during the experiment. Our findings are heterogeneous across households and are mediated by the fit between the preferences of households in our sample for movies and the content available as part of the gifted channels. Households with preferences aligned with the gifted content reduced their probability of using BitTorrent during the experiment by 18% and decreased their amount of upload traffic by 45%. We also show using simulation that the size of the SVoD catalog and licensing window restrictions limit significantly the ability of content providers to match SVoD offerings to the preferences of BitTorrent users. Finally, we estimate that households in our sample are willing to pay at most $3.25 USD per month to access a SVoD catalog as large as Netflix's in the United States. Together, our results show that, as a stand-alone strategy, using legal SVoD to curtail piracy will require, at the minimum, offering content much earlier and at much lower prices than those currently offered in the marketplace, changes that are likely to reduce industry revenue and that may damage overall incentives to produce new content while, at the same time, curbing only a small share of piracy.info:eu-repo/semantics/acceptedVersio